1. Field of the Invention
This invention relates to a manufacturing apparatus for profile extrusion molded articles having a gradually transforming portion at which the cross section thereof is gradually transformed, and a manufacturing method for the same.
2. Description of Related Art
An apparatus has been known from Japanese Patent Unexamined Publication (KOKAI) Heisei 4-338,523 for manufacturing profile extrusion molded articles having a gradually transforming portion at which the cross section thereof is gradually transformed. It includes a stationary die block having a main resin passage, at an outlet of which an aperture is formed in the shape of the maximum cross section of the gradually transforming portion, an extruder for feeding a fixed amount of resin material to the main resin passage, a bypass passage branching off the main resin passage for discharging extra resin material remaining within the main resin passage outside the stationary die block, and a pivotable shutter for changing the aperture size of the main resin passage as well as changing the outlet area size of the bypass passage in correspondence with changing of the main resin passage.
The manufacturing method for profile extrusion molded articles disclosed in the above Publication includes using the manufacturing apparatus described above to perform the steps of feeding a fixed amount of resin material (namely, a resin amount corresponding to the maximum cross section) to the inlet of the main resin passage of the stationary die block, changing the size of the aperture of the main resin passage by rotating the shutter, and thereupon manufacturing the profile extrusion molded articles whose the cross section is gradually transformed. The extra resin material in the main resin passage is discharged outside the stationary die block through the bypass passage.
With this apparatus and method, however, since a fixed amount of resin material is fed to the main resin passage, the extra resin material in the main resin passage must be discharged outside the stationary die block through the bypass passage as described above. Therefore, the bypass passage must be formed in the stationary die block and more resin material is needed than is necessary, so that the apparatus and method tend to be expensive. Moreover, since the shutter gradually changes the aperture size of the outlet of the main resin passage, parting lines tracing the shutter's movement occur on the exposed face of the extrusion molded articles, thereby impairing the appearance of the molded articles.